Cracking Rims

PB Forum :: Mechanics' Lounge
Cracking Rims
Previous Page | Next Page
Author Message
Posted: Sep 15, 2020 at 20:07 Quote
Looking for some insight on aluminum rims. I've cracked a pair a year over the last three years and I'm trying to figure out if I'm doing something wrong. The most recent pair of rims that I cracked were Spank Oozy 350s. Before that was a set of Stans Flow. Both were laced to a set of I9 hubs. When I build the wheels I follow the recommended tension specs on the manufactures website. On the 350s I also used washers.

The failures are always the same. The rim cracks at the nipple hole. By the time I find notice one crack, there are usually multiple when I look closer.

On the 350s I defiantly made sure not to over tension anything (The Flow cracks were fresh in my mind) and I also installed cush core. Brass nipples with DT Swiss Competition Spoke: 2.0/1.8/2.0mm, J-bend.

I'm running Minions with 23-25psi. Trek Remedy 29" with 170mm/150mm front/rear. I weight 165lbs. I ride mainly XC trails on this thing because that's whats in my back yard, but I hammer the down hills (at least in my mind). I'm able to get in about 6-8 days at a bike park a year, and do a few trips a year to some cool riding destinations in the Rockies. I think I got about 1500 miles on these rims before they failed.

Is it normal to go through rims like this? It seems fast to me. Trying to figure out if I'm doing a poor job building them or a poor job of choosing smooth lines!

Posted: Sep 17, 2020 at 14:39 Quote
Very normal depending on the rim. I was cracking e thirteen rims in about three months, all around the nipples. I suggest trying a newmen evolution sl 30 rim. I can get nearly a year out of a rear, they hardly dent either. I weigh 155lbs but ride 3-5 times a week so my bikes do see a bit of wear but these rims are the only ones to last any decent time

Posted: Sep 17, 2020 at 16:00 Quote
It happens, but your failure rate seems high. Thoughts:

• Tension: Most rims list the maximum tension. Is this what you're using as the recommended tension? If so, use a bit less.
• Spoke thickness: Thinner spokes act like a softer springs and reduce maximum loads on the rim. If you aren't having trouble with bending the wheels, use thinner spokes. You can definitely use thinner spokes on the low tension sides of the wheels; maybe also the high tension sides, especially the front wheel.
• Spoke count: If you don't mind using new hubs, a higher spoke count will help, especially if combined with thinner spokes.
• Braking: Locking the wheel (skidding) causes extremely high spoke loads, especially on the disc side spokes that are in higher tension when braking. Are these the ones that are cracking? If so, try to reduce wheel lock-up.
• Lacing: Rims are usually drilled asymmetrically. Ensure the spokes are connected to holes that are angled the proper direction.
• Tire pressure: A minor factor, but if you're running skinny tires and/or old-school pressure, consider larger tires and lower pressure.

Posted: Sep 19, 2020 at 8:20 Quote
Excellent, thanks for the advice!

I'll check out the Evolution sl 30.

- Great call on the tension. I was using the max tension as the target, seems obvious now that you say it, but wasn't thinking about it correctly.
- The torch hubs I've been using are 32 hole, and I have always laced triple cross.
- In the past I was using 2.0mm straight gage, then most recently switched to 2/1.8/2. I'll see if I can go thinner, I like that idea. I don't have trouble bending rims.

Posted: Sep 19, 2020 at 9:42 Quote
eaudiffred wrote:
I'll see if I can go thinner, I like that idea. I don't have trouble bending rims.

Then you can definitely go thinner.

Posted: Sep 19, 2020 at 19:24 Quote
Looks like 5 cracks on the drive side and one on the non-drive.

Posted: Sep 19, 2020 at 23:35 Quote
Working within the constraints of typically available equipment, an ideal set-up would be along the lines of:

• Hubs: large flange offset, especially on the more-constrained sides (front disc and rear drive sides)
• Rim: as much offset as possible
• Spoke count: front: 28; rear: 36
• Spoke thickness: low tension sides: 1.5 mm; high tension sides: usually 1.6 - 1.7 mm with an offset rim or roughly 1.7 - 1.8 mm without an offset rim

The closer you can get to this, the better.

Posted: Sep 20, 2020 at 7:17 Quote
Awesome, thanks for the help!

Previous Page | Next Page

 
Your subscriptions
no posts

Copyright © 2000 - 2020. Pinkbike.com. All rights reserved.
dv56 0.005388
Mobile Version of Website